Pneumatic tire

ABSTRACT

A pneumatic tire has a tread with shoulders, a belt structure located below the tread, and a carcass with two sidewalls, two inextensible annular beads, and a radial ply structure. The shoulders of the tire have a continuous curving radially outer profile so that the shoulders transition smoothly from the tread profile to the tire sidewalls; ideally, the locus of the radii defining the shoulder are located on the inner side of the tire. The tire has a belt structure formed of an annular layer of parallel cords directly adjacent to the radial ply structure, the annular layer having a pair of opposing annular edges and a continuous radius curve profile. Located radially inward of the axial edges of the annular layer of the belt structure is an annular reinforcing strip layer. The strip has a width of not greater than 30 mm and extends axially outward of the annular layer edges by a distance of not more than 10 mm.

RELATED APPLICATION

This is a Continuation of application Ser. No. 10/713,342, filed on Nov.14, 2003, presently pending.

FIELD OF THE INVENTION

The present invention is directed to a pneumatic tire. Morespecifically, the present invention is directed to a belt structureunderlying the tire tread improves the tire's performancecharacteristics for passenger and light truck tires.

BACKGROUND OF THE INVENTION

Almost all pneumatic tires are given a speed rating based on the maximumspeed capability of the tire. The speed rating in conventional use todaywas developed in response to the need to control the safe performance oftires at standardized speeds. When a vehicle manufacturer specifiestires, the required speed rating for the tire is dictated by the type ofvehicle. For a family type sedan car, the speed rating of a tire willlikely be lower than the speed rating for a high performance sports car.Current speed ratings begin at 50 km/h, a B speed rating, and go to a Yor ZR speed rating for tires capable of 300 km/h and above. The majorityof passenger tires have a speed rating of either SR, 180 km/h, or HR,210 km/h.

With an ever increasing interest in high performance sports cars, andthe desire to drive faster, as permitted on parts of the Autobahn inGermany, the goal is to increase the speed performance of the tire.However, as the tire rotates at a faster speed, the centrifugal forceexperienced by the tire and the tire components significantly increases.Designing a tire to compensate and withstand these subjected forces caninvolve modifying many factors, including the belt structure, the moldstructure, and even the footprint shape. As the speed rating increases,small but incremental changes can yield significant increases in thetire performance and increase the tire rating.

Another desired change in conventional tires is the need for a tire tobe capable of operating when in reduced pressure conditions, i.e. arun-flat tire. The majority of run-flat tires in the market place areself-supporting run-flat tires. Such tires are provided with increasedthickness sidewalls that support the tire during reduced pressureconditions. The increased sidewall thickness, achieved by the use ofadditional rubber layers in the sidewall, can reduce a tires speedrating because of the greater weight and internal heat generated by thetire. Thus, the need to have a run-flat tire also affects the normaloperation of the tire by reducing the tire's capability.

SUMMARY OF THE INVENTION

One aspect of the invention is directed to achieving an improved speedperformance and improved durability of a tire. Another aspect of theinvention is directed to the conflicting goals of a run-flat tire withhigh speed capability, thus providing persons with high performancevehicles with the desired full inflation performance expected anddemanded from their vehicle and with assurance that the tire willcontinue to perform in atypical reduced pressure situations.

Disclosed is a pneumatic tire having a tread with shoulders, a beltstructure located below the tread, and a carcass with two sidewalls, twoinextensible annular beads, and a radial ply structure. The shoulders ofthe tire have a continuous curving radially outer profile so that theshoulders transition smoothly from the tread profile to the tiresidewalls; ideally, the locus of the radii defining the shoulder arelocated on the inner side of the tire. This is distinct from a shoulderhave a square shoulder, where the tread comes to an abrupt end hard edgebefore transitioning into the upper sidewall of the tire. The inventivetire further has a belt structure formed of an annular layer of parallelcords directly adjacent to the radial ply structure, the annular layerhaving a pair of opposing annular edges and a continuous radius curveprofile. Located radially inward of the axial edges of the annular layerof the belt structure, and directly adjacent along the axial edges ofthe annular layer, is an annular reinforcing strip layer. The strip hasa width, defined between terminal ends thereof, of not greater than 30mm and one terminal end of the strip layer extends axially outward ofthe annular layer edges by a distance of not more than 10 mm.

In one disclosed aspect of the tire, the annular reinforcing strip layeris comprised of cords, the cord material selected from a group ofmaterial consisting of nylon, rayon, polyester, aramid, metal, andglass. The cords are inclined at angles of 0° to 5° relative to acenterline of the tire.

In another aspect of the tire, the belt structure includes an overlayply. The overlay ply is radially outward of the annular layer ofparallel cords and has a width greater than the annular layer ofparallel cords. The annular reinforcing strip layer may be formed fromthe same cords as the overlay ply, or the strip may be formed fromdifferent types of cords.

In another aspect of the tire, the annular reinforcing strip layer usedin the tire has a width of 20, 10, or 5 mm. The strip extends past thebelt edges by a distance of not more than either 10 mm, preferably 6 mm,or 75% of the width of the reinforcing strip layer, whichever is thelesser of the two values.

In another aspect of the present invention, the belt structure of thetire has a belt width of at least 95% of the tread width. At the axiallyouter ends of the belt structure, the annular layers forming the beltstructure have a belt ply drop of not more than 6 mm, and ideally have abelt ply drop of not more than 2 mm.

In another aspect of the present invention, the tire with the annularreinforcing strip layers may be a self-supporting run flat tire. Thetire has at least one rubber insert located in the sidewall of the tire,axially inward of the radial ply structure. The rubber insert has aShore A hardness in the range of 45 to 90 at 100° C.

Definitions

The following definitions are controlling for the disclosed invention.

“Apex” means an elastomeric filler located radially above the bead coreand between the plies and the turnup ply.

“Annular” means formed like a ring.

“Aspect ratio” of the tire means the ratio of its section height to itssection width multiplied by 100% for expression as a percentage.

“Axial” and “axially” means lines or directions that are parallel to theaxis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim. The radially inner beads are associated with holdingthe tire to the wheel rim.

“Belt structure” means at least one annular layers or plies of parallelcords, woven or unwoven, underlying the tread, unanchored to the bead,and having both cord angles in the range from 17° to 28° with respect tothe equatorial plane of the tire.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tire parallel to the EquatorialPlane (EP) and perpendicular to the axial direction.

“Contact Patch” means a section of footprint, in a footprint that isdivided into sections by wide void areas, that maintains contact withthe ground.

“Design rim” means a rim having a specified configuration and width. Forthe purposes of this specification, the design rim and design rim widthare as specified by the industry standards in effect in the location inwhich the tire is made. For example, in the United States, the designrims are as specified by the Tire and Rim Association. In Europe, therims are as specified in the European Tyre and Rim TechnicalOrganization—Standards Manual and the term design rim means the same asthe standard measurement rims. In Japan, the standard organization isThe Japan Automobile Tire Manufacturer's Association.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure.

“Inner” means toward the inside of the tire and “outer” means toward itsexterior.

“Lateral” means an axial direction.

“Lateral Edge” means the axially outermost edge of the tread as definedby a plane parallel to the equatorial plane and intersecting the outerends of the axially outermost traction lugs at the radial height of theinner tread surface.

“Normal Inflation Pressure” means a specific design inflation pressureand load assigned by the appropriate stands organization for the servicecondition for the tire.

“Outer” means toward the tire's exterior.

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire.

“Shoulder” means the upper portion of sidewall just below the treadedge, effects cornering. Tread shoulder or shoulder rib means thatportion of the tread near the shoulder.

“Sidewall” means that portion of a tire between the tread and the bead.

“Tread Pressure” means the distribution of load across the footprintarea of tire.

“Tread Width” means the arc length of the tread surface in the axialdirection, that is, in a plane parallel to the axis of rotation of thetire.

“Turn-up ply” means an end of a carcass ply that wraps around one beadonly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying FIGURE in which is illustrated a cross sectional viewof a tire half in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following language is of the best presently contemplated mode ormodes of carrying out the invention. This description is made for thepurpose of illustrating the general principles of the invention andshould not be taken in a limiting sense. The scope of the invention isbest determined by reference to the appended claims.

Based on conventional manufacturing sequences, there are two basic partsof pneumatic radial ply tires used on cars and trucks. One part is thecarcass, typically assembled on a cylindrical building drum prior toexpansion. The carcass includes the reinforcing plies, two inextensibleannular beads, sidewalls, the innerliner, and the elastomeric materialthat holds those components together after the tire is assembled and thecarcass is cured. The other part of the tire is the crown, which isassembled separately from the carcass and includes the tread and theunderlying belts or breakers, also held together by a matrix of curedrubber. The carcass is joined with the crown before being cured underpressure in a heated press that, as well as curing the rubber, impressesthe tread pattern into the radially outermost rubber and also createsany desired sidewall patterns and required indicia on the sidewalls.

In such a generalized or generic tire, the belts or breakers, which aremost often made of steel or other essentially inextensible material, arepart of the crown assembly and are disposed immediately adjacent to,though radially outward of, the ply layers of the carcass.

Referring now to the FIGURE, there is shown in cross sectional view asegment of a molded self-supporting radial ply tire 10 incorporating anaspect of the present invention. The non-illustrated half of the tire 10is symmetrical to that illustrated. The carcass has at least one radialply layer forming the primary reinforcing structure to the tire. In theillustrated tire, the carcass has an outer radial ply layer 12, an innerradial ply layer 14, together comprising a radial ply structure. The endof the inner radial ply layer 14 is wrapped about an inextensibleannular bead 16 with the terminal ends of the ply layer being radiallyinward and axially outward of the belt structure 24. To space theturn-up ply 18 of the inner radial ply layer 14 from the outer radialply layer 12, an apex 20 may be placed radially outward of the annularbead 16. Radially inward of the ply layers 12, 14, in each sidewall is asidewall wedge insert 22. The sidewall wedge insert 22 provides the tirewith run-flat, self-supporting capabilities. Such items are known in theart and will not be discussed at length herein. Though FIG. 1 shows aself-supporting run-flat tire design, it is also contemplated by theinventors to incorporate the present invention in non self-supportingtype tires or other type of run-flat tires. The tire structure would beas discussed above and below, sans the wedge insert 22.

A belt structure 24 and a tread 26 are radially outward of the carcassply layers 12, 14. The belt structure 24 has at least one radiallyinnermost ply 28 of parallel cords that is directly adjacent to theoutermost radial ply layer 12 for the majority of its axial width.Outward of the innermost ply 28 may be at least one more ply 30 ofparallel cords, as illustrated. The parallel cords of the adjacent layer30 are preferably inclined at an equal angle but opposite hand from theinclination of the cords in the innermost ply 28.

In the lateral regions of the radially innermost belt ply 28, the beltply 28 is distanced from the carcass plies 12, 14 as the carcass plypath follows the outer contour of the run-flat insert 22. In the outer20% of the belt width BW the belt plies 28, 30 curve radially inward.The belt ply drop C is defined as the drop of the centerline of the beltstructure 24 from a point at 20% of the belt width BW to the axiallyoutermost point of the belt center line. The belt ply drop C influencesheel and toe wear of a tire. A lower belt ply drop C improves the heeland toe wear of the tread. Preferably, the belt ply drop C is less than6 mm and more preferably, the belt ply drop C is less than 2 mm.

The belt structure 24 has a width BW of at least 95% of the tread widthTW. The tread width TW is measured from the shoulder drop point P alongthe outer profile of the tire 10. A wider belt structure 24 increasesthe high speed performance of a tire, but necessitates a way of keepingthe belt edges at the desired profile and a minimized belt ply drop C.

The outer surface of the tread 26 is defined by a smoothly continuousprofile. The tread 26 is illustrated with no grooves, however, thoseskilled in the art will appreciate that the tread 26 may be grooved inany number of tread patterns. Whatever groove pattern is selected, theupper surface of the tread 26 will have the disclosed surface profile.In the central region of the tread, the profile defined by a radius ofcurvature RT which is preferably similar to the belt profile curvature,creating a substantially constant tread thickness. At the tread edges,in the shoulders of the tire, the tread thickness decreases, and theradii defining the tread profile may decrease.

To maintain the spacing between the lateral edges of the belt structure24 and the carcass plies 12, 14 in the shoulder region of the tire,conventionally, a rubber wedge is inserted into the spacing. Inaccordance with an aspect of the present invention, to improve the highspeed durability of the tire 10, the spacing is partly maintained by anannular reinforcing strip layer 32 located radially inward of thelateral edges of the radially innermost belt layer 28. The reinforcingstrip layer 32 has a width U that prevents the belt layers 28, 30 fromlifting at the inside edge 34 of the reinforcing strip layer.Preferably, the strip layer 32 has a width U of at least 5 mm and notgreater than 30 mm, preferably not more than 20 mm. If the width U ofthe layer 32 is greater than 30 mm, a bend in the belt structure 24 maybe created.

The reinforcing strip layer 32 is formed of at least one ply of parallelreinforcing cords inclined at 0° to 5° relative to the centerline of thetire 10. The cords may be formed of any conventional tire cordmaterials, such as, but not limited to, nylon, rayon, polyester, aramid,metal, or glass. The cords should be formed as high elongation cords,i.e. having a relative elongation of at least 4% when under a tensileforce equal to the breaking load. The reinforcing strip layer 32 may beformed from the same material used as an overlay ply, if an overlay plyis present in the belt structure 24. To obtain the width U of at least 5mm and not greater than 30 mm, the layer 32 may be formed of adjacentsmaller width strips, such as 4 strips of 5 mm wide plies to form areinforcing strip layer of 20 mm width.

The reinforcing strip layer 32 extends axially outward of the innermostbelt ply by a distance V. The strip layer 32 preferably extends outwardfrom the belt structure 24 by no more than 10 mm, preferably not morethan 6 mm, regardless of the width U of the strip layer 32.Additionally, the strip layer 32 should extend past the belt structure24 by a width V of not more than 75% of the strip width U. The amount ofthe extension width V will be whichever is the lesser value. Forexample, when the strip layer 32 has a width U of 5 mm, the extensionwidth V should not be greater than 75% or 3.75 mm. When the strip layer32 has a width of 20 mm, the extension width V is not more than 10 mm,or 50% of the strip layer width U and when the strip layer 32 has awidth U of 30 mm, the strip layer 32 has an extension width V of notmore than 10 mm, or 33% of the strip layer width V.

By providing the annular reinforcing strip layer 32 under the lateraledge of the innermost belt layer 28, endurance characteristics of thetire 10 are improved.

In testing, three tires A, C, E were constructed in accordance with thepresent invention and as illustrated in the FIGURE, were comparedagainst control tires, B, D, F. The comparative tires had a similarcarcass construction to the same sized inventive tires and had annularreinforcing strip layers over the belt structure in the shoulder regionof the tires in the manner noted in the Table. The inventive tires andcomparative tires were tested and the results are set forth below.

A B C D E F Tire size 225/35ZR19* 225/35ZR19* 225/35ZR19* 225/35ZR19*235/40ZR18** 235/40ZR18** Reinforcing strip layer Width,  20  20  15  15 10  10 mm Location in shoulder, under in shoulder, under In shoulder,under above belt innermost belt above belt innermost belt above beltplies innermost belt plies ply ending plies ply ending ply ending HighSpeed Performance Max 340 350 340 350 290 300 Speed, km/h Time at 35seconds 5 minutes 3 minutes 4 minutes 6 minutes 6 minutes Max Speed*Test Conditions: load: 432 kg; inflation: 2.7 bar; 1.2° camber angle;8.5″ rim **Test Conditions: load: 431 kg; inflation 3.0 bar; 4° camberangle; 9″ rim

The speed tests were an incremental step speed test performed in thefollowing manner: 5 minutes at 210 km/h; 30 minutes at 240 km/h; 30minutes at 270 km/h; 10 minutes at 280 km/h; 10 minutes at 290 km/h.Once the tire had performed at 290 km/h for the ten minutes, the speedwas increased by 10 km/h and then by another 10 km/h every ten minutesthereafter until tire failure was achieved.

The test results show that a higher maximum speed and time at maximumspeed are achieved when the reinforcing strip layer 32 is radiallyinward of the belt ply endings as shown in the FIGURE rather than such alayer being located above the belt structure 24. Additionally, the speedincreases for increased width of the strip layer 32.

The reason for the increased maximum speed may be as follows. Tirefailure is usually caused by two factors: a standing wave generated bythe centrifugal force or heat buildup in the tire. If the generation ofthe standing wave can be pushed to a higher speed and the internal tiretemperature controlled, then the tire will perform for a longer time andwill be capable of higher speeds. In the inventive tire, mitigation ofboth factors occurs. The presence of the annular reinforcing strip layermaintains the belt profile in a desired flatter profile, pushing out thestanding wave generation. Additionally, by replacing some of the rubberof the typical shoulder wedge under the belt edge, the amount of rubberin the shoulder region is reduced, decreasing the heat buildup.

Due to the presence of the annular reinforcing strip layer 32, thefootprint shape factor is also increased. Footprint shape factor (FSF)is the ratio of the footprint length at the center of the tread to thefootprint length at the tread edges. To calculate FSF, the maximum axialwidth W of the footprint is first measured. Then, the distance halfwaybetween the maximum axial width W is defined as the tire's centerplaneCP. A distance 40% of the tread width (W) on each side of thecenterplane is located and lines parallel to the tire's centerplane aredrawn. The length of the parallel lines is calculated, summed, anddivided by 2 to arrive at an average shoulder length L_(S). Thefootprint length L_(C) at the centerplane is measured. The footprintshape factor F is the ratio of L_(C)/L_(S).

The observed increase in the FSF is believed to be due to an increasedrestraint of the belt plies 28, 30 at the shoulder edges. While anoverlay layer outward of such belt plies 28, 30 acts to restrain radialgrowth of the belt structure 24 and the belt edges, the annularreinforcing strip layer 32 acts to restrain radial growth of the carcassplies 12, 14 in the shoulder region and to maintain a desired belt edgeprofile.

1-10. (canceled)
 11. A pneumatic runflat tire, the tire comprising atread with shoulders, a belt structure located below the tread, and acarcass with a radial ply structure and terminal ends located axiallyoutward and radially inward of the belt structure, two sidewalls, atleast one rubber insert axially inward of the radial ply structure ineach sidewall, and two inextensible annular beads, the tirecharacterized by: the shoulders each having a continuous curvingradially outer profile; the belt structure comprising an annular layerof parallel cords directly adjacent to the radial ply structure, theannular layer having a pair of opposing annular edges and a continuousradius curve profile; an annular reinforcing strip layer locatedradially inward and directly adjacent of each annular layer edge alongthe edge of each annular layer, each strip having a width of not greaterthan 20 mm as measured between terminal ends of the strip layer, and oneterminal end of the strip layer extending axially outward of the beltstructure, the axial extension of the strip layer being greater than 0mm and not more than 10 mm, the amount of axial extension of the striplayer being 75% of the width of the strip layer.
 12. The tire of claim11 wherein the annular reinforcing strip layer is comprised of cordsinclined at an angle of 0° to 5° relative to a centerline of a tire. 13.The tire of claim 11 wherein the belt structure further includes anoverlay ply located radially outward of the annular layer of parallelcords, the overlay having a width greater than the annular layer ofparallel cords.
 14. The tire of claim 13 wherein the annular reinforcingstrip layer is formed of the same cords as the overlay ply.
 15. The tireof claim 11 wherein the annular reinforcing strip layer has a width of15 mm.
 16. The tire of claim 11 wherein the annular reinforcing strip iscomprised of cords, the cords having a relative elongation of at least4% when under a tensile force equal to the cord breaking load. 17.(canceled)